[Hey_You]

What exactly happens in the following conditions:
1. The Power of a machining center for a specific operation is sufficient, but its Torque isn't sufficient.
2. The Torque of a machining center for a specific operation is sufficient, but its Power isn't sufficient.
Why is it said that the torque of a machine is a more important factor than its power?

Source: Destiny Tool: End Mill Performance & Spindle Torque

[joeavaerage]

Hi,'
torque is effectively the force that the spindle can apply to 'push' the tool tooth through the material and 'peel' off a chip.
If the spindle does not have enough torque to remove a chip, because the chip is too big, or the material is just too tough
then the spindle will stall. That's a real problem because in a CNC machine the toolpath is advancing whether the spindle spins or not, and so the
machine is just going to push like hell until either it stalls the axis OR the tool snaps, usually the later.

I have a small 800W 24000rpm spindle that I use it a lot....it's great.... but it's not much good in steel. This is because it has so little torque. If you try to take a decent cut
you risk the tool stalling and shortly thereafter the tool will be broken, unless you can hit the <Stop> button fast enough.

On the other hand, if a spindle has plenty of torque but not much power, basically means it spins slowly. It's got enough torque and it will peel off say 0.1mm thick chips without
any risk of stalling but can only advance 0.1mm per tooth per rev....so is likely to be slow.

Power, speed and torque are related:

Power = Torque x Speed. I use metric units so the equation is:

Power (in Watts)= Torque (in Newtons per meter) x Speed (in radians per second, where one revolution is equal to 2xPI radians)

As an example say we have a motor that can produce 5Nm of torque at 1500rpm:
Speed= (1500 / 60) x 2 x PI
=157.07 radians/sec

Power = 5 x 157.07
=785.4 W.....which is just a fraction over 1 hp.

Lets say that we find that 5Nm is not enough to reliably drive a tool in a really tough piece of steel. What we choose to do is run the same 1hp motor but through a belt and pulleys
to increase the torque. Lets say that the belt reduction is 2:1

Spindle speed= motor speed /2
=157.07/2
=78.5 radins /sec

Torque = Power / Speed
= 785.4 / 78.5
=10 Nm

So as we expect the belt reduction has halved the speed, but now has twice the torque so the power remains 1 hp. Now we can bore into that piece of steel and be sure that the torque of the spindle
is sufficient to peel off chips, whereas before with just 5Nm the spindle could and sometimes would stall and bad things would happen There is no free lunch though, sure, we have more torque
but we can only go half as fast.

Why is it said that the torque of a machine is a more important factor than its power?

The torque of a spindle determines if it has the grunt to do the job at all, and the power determines how fast it can do it.

Craig

[Hey_You]

Hi,'
torque is effectively the force that the spindle can apply to 'push' the tool tooth through the material and 'peel' off a chip.
If the spindle does not have enough torque to remove a chip, because the chip is too big, or the material is just too tough
then the spindle will stall. That's a real problem because in a CNC machine the toolpath is advancing whether the spindle spins or not, and so the
machine is just going to push like hell until either it stalls the axis OR the tool snaps, usually the later.

I have a small 800W 24000rpm spindle that I use it a lot....it's great.... but it's not much good in steel. This is because it has so little torque. If you try to take a decent cut
you risk the tool stalling and shortly thereafter the tool will be broken, unless you can hit the <Stop> button fast enough.

On the other hand, if a spindle has plenty of torque but not much power, basically means it spins slowly. It's got enough torque and it will peel off say 0.1mm thick chips without
any risk of stalling but can only advance 0.1mm per tooth per rev....so is likely to be slow.

Power, speed and torque are related:

Power = Torque x Speed. I use metric units so the equation is:

Power (in Watts)= Torque (in Newtons per meter) x Speed (in radians per second, where one revolution is equal to 2xPI radians)

As an example say we have a motor that can produce 5Nm of torque at 1500rpm:
Speed= (1500 / 60) x 2 x PI
=157.07 radians/sec

Power = 5 x 157.07
=785.4 W.....which is just a fraction over 1 hp.

Lets say that we find that 5Nm is not enough to reliably drive a tool in a really tough piece of steel. What we choose to do is run the same 1hp motor but through a belt and pulleys
to increase the torque. Lets say that the belt reduction is 2:1

Spindle speed= motor speed /2
=157.07/2
=78.5 radins /sec

Torque = Power / Speed
= 785.4 / 78.5
=10 Nm

So as we expect the belt reduction has halved the speed, but now has twice the torque so the power remains 1 hp. Now we can bore into that piece of steel and be sure that the torque of the spindle
is sufficient to peel off chips, whereas before with just 5Nm the spindle could and sometimes would stall and bad things would happen There is no free lunch though, sure, we have more torque
but we can only go half as fast.



The torque of a spindle determines if it has the grunt to do the job at all, and the power determines how fast it can do it.

Craig

Thanx for your comprehensive answer.

[peteeng]

Hi Hey answers:-
1) The tool stalls as it cannot create a force big enough to cut (shear) the material
2) The tool can cut the material but the feed rate is limited to the power available. Power= force x velocity so double the power, double the velocity (feed rate) roughly
3) The torque is doing the cutting the power is doing the moving. Its more important to cut then move.

See diagram attached. The tool creates a force at the tooth of the tool. This force is the spindle torque divided by the radius of the tool. This has to be greater than the resistance of the material to chip. ie the shear strength of the material or the force to create the chip. This is analogous to the break away torque on a rusty nut say.

In a commercial situation maximising material removal is required to make money so powerful spindles are used so they can feed at very high rates. In a hobby situation MRR is less important so spindles are smaller. But they do need to be big enough to do the job. Plastics, timber, metals all require different spindle power/torques as they have different material shear strengths. Peter

[deadlykitten]

hy as shown attached, a machine producer can give you such a spindle diagram

let's supose you have a repetable setup, same fixture, tool, and cutting specs, and simply wish to get another machine

comparing both diagrams, at the same rpm, can give you a glance about how much you are pushing each machine; as you allready have experience with your actual machine, you can evaluate the spindle of another machine

basically, it tells you how much you are pushing the spindle, and the spindle only, because is no guarantee that the structure of the machine is better ?! at least should be

okuma machines can display such data live, as you cut it, so to give you a hint on where you are on machine capability scale

you push it harder, you need more torque available, at the cost of grid power ... simple as that

for example, you can balance required torque, only by changing inserts :
... obvious example, from wear, to new ones
... less obvious, from tough edge, to low force feed / kindly

[Hey_You]

appreciate your attentions